In Intensity Modulated Radiation Therapy (IMRT), the use of non-coplanar beams yields treatment plans with improved organ sparing compared to coplanar plans. Current radiotherapy planning systems have limited support for optimizing non-coplanar incident beam directions in general. This is due in at least part to the combinatorial nature of the problem. Current approaches such as simulated annealing or integer programming are too computationally expensive to be used in practice.
Volumetric Modulated Arc Therapy (VMAT) refers to radiotherapy treatments in which the treatment beam continuously transmits while the gantry (and hence the treatment beam) rotates. VMAT allows for reduced treatment time by delivering radiation while the gantry moves around the patient. Unfortunately, VMAT delivery has been restricted to coplanar beams, for example, realized by a fixed couch angle, such as zero.